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Single dose oral aspirin for acute postoperative pain in adults

Aspirin is commonly used throughout the world as an over the counter (OTC) analgesic medication used to treat various painful conditions and to reduce fever. This review assessed both the pain-relieving effectiveness and the adverse effects of a single dose of aspirin in acutepostoperative pain of moderate to severe intensity. We included 67 studies, with 3111 participants given aspirin in comparisons with 2632 given placebo. Most of the information was for a 600 mg or 650 mg dose. The results confirm that in patients with moderate to severe postoperative pain, about 40% of those treated with aspirin 600/650 mg will experience good levels of pain relief, compared with about 15% treated with placebo. This level of pain relief is comparable to that experienced with the same dose of paracetamol. In these single dose studies there was no significant difference between aspirin 600/650 mg and placebo for the number of participants experiencing adverse events, but at 900/1000 mg, twice as many did so, with dizziness, drowsiness, gastric irritation, nausea, and vomiting being the most common events reported.

Authors' conclusions:

Aspirin is an effective analgesic for acute pain of moderate to severe intensity. High doses are more effective, but are associated with increased adverse events, including drowsiness and gastric irritation. The pain relief achieved with aspirin was very similar milligram for milligram to that seen with paracetamol. There was no change to the conclusions in this update.

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Background:

This review is an update of a previously published review in the Cochrane Database of Systematic Reviews on 'Single dose oral aspirin for acute pain'. Aspirin has been known for many years to be an effective analgesic for many different pain conditions. Although its use as an analgesic is now limited in developed countries, it is widely available, inexpensive, and remains commonly used throughout the world.

Objectives:

To assess the analgesicefficacy and associated adverse events of single dose oral aspirin in acutepostoperative pain.

Search strategy:

For the earlier review, we identified randomised trials by searching CENTRAL (The Cochrane Library) (1998, Issue 1), MEDLINE (1966 to March 1998), EMBASE (1980 to January 1998), and the Oxford Pain Relief Database (1950 to 1994). We updated searches of CENTRAL, MEDLINE, and EMBASE to January 2012.

Selection criteria:

Single oral dose, randomised, double-blind, placebo-controlled trials of aspirin for relief of established moderate to severe postoperative pain in adults.

Data collection and analysis:

We assessed studies for methodological quality and two review authors extracted the data independently. We used summed total pain relief (TOTPAR) over four to six hours to calculate the number of participants achieving at least 50% pain relief. We used these derived results to calculate, with 95% confidence intervals, the relative benefit compared to placebo, and the number needed to treat (NNT) for one participant to experience at least 50% pain relief over four to six hours. We sought numbers of participants using rescue medication over specified time periods, and time to use of rescue medication, as additional measures of efficacy. We collected information on adverse events and withdrawals.

Main results:

We included 68 studies in which aspirin was used at doses from 300 mg to 1200 mg, but the vast majority of participants received either 600/650 mg (2409 participants, 64 studies) or 990/1000 mg (380 participants, eight studies). There was only one new study.

Studies were overwhelmingly of adequate or good methodological quality. NNTs for at least 50% pain relief over four to six hours were 4.2 (3.9 to 4.8), 3.8 (3.0 to 5.1), and 2.7 (2.0 to 3.8) for 600/650 mg, 900/1000 mg, and 1200 mg respectively, compared with placebo. Type of pain model had no significant impact on the results. Lower doses were not significantly different from placebo. These results do not differ from those of the earlier review.

Fewer participants required rescue medication with aspirin than with placebo over four to eight hours postdose, but by 12 hours there was no difference. The number of participants experiencing adverse events was not significantly different from placebo for 600/650 mg aspirin, but for 900/1000 mg the number needed to treat to harm was 7.5 (4.8 to 17). The most commonly reported events were dizziness, drowsiness, gastric irritation, nausea, and vomiting, nearly all of which were of mild to moderate severity.